This invention relates to an improved method of silver-plating stainless steel vacuum bottle surfaces.
Vacuum bottles are conventionally comprised of spaced apart inner and outer bottles so that the volume therebetween can be evacuated to form a vacuum chamber for insulating the structure's contents against gas conduction.
Conventionally, one or both of the vacuum chamber walls are reflectorized in order to reduce radiation heat loss. This reflectorization is commonly accomplished by silvering or by aluminum or nickel plating or by precision-polishing the vacuum chamber walls in order to improve their reflectivity. In order to improve the durability of vacuum bottles, however, the bottles have been made of stainless steel or other metals. But it has been difficult to plate such stainless steel walls with silver, because existing techniques for electroless plating have tended to result in an overly thick coating of silver which is prone to containing defects even when the stainless steel surfaces are first chemically or mechanically treated.
Accordingly, aluminum or nickel plating and the like have been replacing silver plating even though silvered surfaces provide improved reflectivity.
It is an object of this invention, therefore, to provide a method for depositing very thin, uniform, defectless silver coating directly onto stainless steel vacuum chamber surfaces.
One method of depositing silver onto stainless steel vacuum chamber walls has been to first place a layer of glass on the stainless steel walls or to first plate the stainless steel with nickel or the like. These methods, however, add process steps to the manufacture or the vacuum bottle and result in higher manufacturing costs. Additionally, the thickness of the metal or glass plating layers provides additional locations for gas molecules which tend to degrade the vacuum in the vacuum chamber and increase heat losses caused by the transport of heat by those gas molecules. Accordingly, it is yet another object of the present invention to provide a method of silverplating stainless steel vacuum chamber walls wherein manufacturing costs are reduced without increasing heat losses by radiation and/or gas conduction.